Electromagnetic deflecting yoke and circuit



June 8, 1948. R. B. GETHMANN 2,443,032

ELECTROMAGNETIC DEFLECTING YOKE AND CIRCUIT Filed Oct. 29, 1946 Fig. 2..

n v .4 n h e O t B A 0 2 n v 1w 9 1% H a R M m an m Wn m a 6.3/49 4 Wm M\ a I 3 u ,5 m w E w 2 F n Q as Patented June 8, 1948 ELECTROMAGNETIC DEFLECTIN YOKE AND CIRCUIT Richard Barton Gethmann, Bridgeport, Conn,

assignor to General Electric Company, a corporation of New York Application October 29, 1946,. Serial No. 706,461

My invention relates to structures fof'deflecting the electronic beam of a cathode ray tube and, in particular, to such structures employing a magnetic yoke and coils for establishing transverse magnetic fields to deflect such a beam.

In equipment for locating the position of an object by means of radio waves, it is customary to employ a cathode ray tube and to use signals received from an object in space to be located to deflect the electronic beam of such a tube to a position which indicates, on the fluorescent end wall of the tube, the location of the object. Such deflection of a cathode ray beam may be effected by either electrostatic or magnetic fields. One of the diificulties encountered when employing magnetic fields for such purposes is obtaining structures which give a linear field across the neck of the cathode ray tube. The usual structure employed produces a field which curvesoutwardly from a plane longitudinal of the neck of the tube. It is an object of my invention to provide a new and improved magnetic yoke and circuit for a cathode ray tube which provides a substantially linear magnetic field.

It is still another object of my invention to provides. new and improved magnetic yoke for deflecting a cathode ray beam in which a cross magnetic field is used to improve the linearity of the resultant magnetic field.

According to one feature of my invention, I provide a magnetic core formed of pairs of parallel legs arranged to form a square. The winding disposed on each leg consists of a pair of outer coils and a pair of intermediate coils. Circuits for deflecting the cathode ray beam in substantially perpendicular directions are formed by connecting the outer coils of two parallel legs in series circuit with the intermediate coils on the legs transverse to the two legs, the outer coils being connected to establish opposing magnetic fields in a direction transverse to the principal field established by the intermediate coils so that a substantially uniform linear resultant field is obtained.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a vertical elevation view of a cathode ray tube employing the sweep yoke of my invention; Fig. 2 is a vertical eleva- 7 Claims. (01. 250--157) CPI ' sequence opposite to their numerical order.

tion view showing the location and the circuit connection of the coils of the improved sweep: yoke; Fig. 3 is a diagram illustrating the flux pattern of one of the deflecting circuits of the structure of Fig.2; and Fig. 4 illustrates certain operational characteristics of the structure of Fi 1.

Referring to the drawing, I have shown in Fig. 1 a cathode ray tube I having the usual fluorescent end wall 2 and including a cathode 3' and at least one control electrode 4. The cathode ray tube I may be conventional in structureand forms no part of my present invention. In such a tube it is customary to establish an electron beam in the tube by suitably heating the cathode 3 and establishing an electric field between the cathode 3 and an anode, not shown. When such a tube is employed, in either television receivers or equipment for locating an object in space, it is customary to employ means to deflect the cathode ray beam in accordance with variations of received signals. Accordingly, the cathode ray tube I is provided with a deflecting structure 5,. the details of which are shown in Fig. 2.

The deflecting structure 5 shown in Fig. 2 comprises a magnetic core 6 formed of any suitable material, such as a high permeability steel. The core 6 is substantially square in cross section having four rectangularly disposed legs 'I-IIl. Each of the legs I-IIl is encircled by an insulating material, such as the insulating tubes II. Supported on the tubes I I on each of the legs are eight coils, coils I2-I9 being supported on leg I, coils 2Il2l being supported on leg 8, coils 2835 being supported on leg 9, and coils 36-43 being supported on leg III. In order to establish two transverse magnetic fields between opposite of the legs, which fields are substantially linear across the gap between parallel legs, I connect the intermediate coils on parallel legs in series circuit with the end or outer coils on the legs adjacent to the parallel legs. Thus, the series circuit which establishes a uniform magnetic field across the gap between legs 8, II] is connected between terminals 44, 45 and comprises coils 43, l3-I8, 20, 36, 2934, and 21, the coils 29-44 being connected in the series circuit in a The other series circuit, which extends between terminals 46, 41 and which establishes a uniform magnetic field across the gap between legs I, 9 comprises coils I9, 2I26, 28, I2, 3l42, and 35. In this circuit the coils 3I42 are connected in a sequence opposite to that indicated by their numerical order. This reverse connection of coils 3 25-44 and 31-42 is required in order that the fields established by these coils have the same polarity as those established by the coils on the opposite parallel legs.

The advantages effected by my improved coil arrangement may better be explained by reference to the flux diagram of Fig. 3 which illustrates, in theupper half thereof, the flux pattern of the coils 13-18, 20, and 43 and, in the lower half, the resultant flux of the coils 21, 29-44, and 36. In the upper half of the, diagram of Fig. 3, the magnetic field due to coils 13-11115 shown in full line, while the magnetic field due to the coils in and 43 is shown in broken; line. The resultant field of the coils -I 3l8 andflland 43 is a mirror image of that shown in the lower half of Fig. 3. This resultant field is substantially linear and uniform between the legs 8, [0. As a result, it may be employed for horizontal deflection of the electron beam of the cathode raybcam. The strength-of the field, of course, depends uponthe current-passing through the seriescircuit. between the terminals 44; 45, and the number of turns in this series circuit.

1 Fromzthe flux pattern of Fig. 3, it is apparent .-that.the coils on any one leg produce a-field which curves toward the ends of that leg. Thus, the solid .lines on the upper portion of Fig. 3, at

their outer ends, curve upwardly toward the ends 19K:

The coils 20 and 43pm the adjacent legs produce a transverse or cross field which is just sufficient to compensate for the non-linearities in the field produced by the coils l3-(l8. It is .aparent that, when all of the windingsof the deflection circuit are concentrated on one leg or two parallel legs; it is. never possible to get a .uniform field parallelwith those legs.

However, the .field may. be made uniform by the addition of coils on the adjacent leg.

.Inconstructing a core according to myinvention, the coils on any one leg may either be given the same number of turns or the number of turns on adjacent coils may be varied in order to produce a desired field pattern. Thus, the shape of the resultant fiux may be controlled in part -by increasing the number of turnsper coil for .coils further from the axis of the yoke.

Thus, the coils I5, [6 may, for example, be given the some number of turns, while the number of turns may be increased for the coils l4, l1 and furtherincreased for coils I3, .18 in order that the fieldbe uniform across'the neck of a cathode ray tube. The same variation may be given to coils 29-44.

"The effect of increase inthe number of turns.

percoil is better illustrated by reference to Fig. 4 in which curve48 illustrates the curvature of the field ofa yoke constructed as illustrated in Fig. 2 and in which the turns on coils l3 and I8 aresubstantially twice the number of those on coils l5, l6, while coils l4, l1 have approximately an intermediate number of turns.

Curve 49, which is substantially linear, illustrates the field pattern when the same number of turns is used and no compensating windings. are employed.

I have found that a uniform field may be obtained only through the use of compensating coils as described above. Since in some cathode ray tubes the smallest amount of astigmatism is obtained only when a uniform field is employed, it is apparent that my improved electromagnetic deflecting yoke and circuit provides desired improvements of the beam deflecting structures for such tubes. In other cathode ray tubes, especially tubes of large size or those having a large radius of curvature of the end wall, a certain .amount'of non-linearity may be desired for focusing purposes. By my invention any desired configurationof field, whether that configuration be linear or. acurvature in a direction not hereto- --fore possible, may be obtained by choosing the ratio of the number of turns of the coils providing the primary deflecting fields and the construction of the coils providing the compensating fields to control the intensity of such a compensating or transverse field.

An important advantage of my invention is that itprovides a magnetic fieldior deflecting the electron beam of a cathode ray tube,- which field is substantially linear across the neckof: the cathode ray tube. The exact curvature-may be controlled by controlling the number fofrturns for the variouscoils in any one series circuit.

While I have shown and described one-aparticular embodiment of my invention, it-,wlll of course-beapparent to those skilled in the'art that changes and modifications may be made without departing from my invention. Lthereforehaim in the appended claims to cover all such changes and modifications as fall within the true :spirit and scope'of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a deflection yoke for a cathode rayqtube, a magnetic core having four'legs arranged to form a rectangle, a plurality of coils supported on each of said legs, the outer coils on each of said legs being connected in series circuit withxthe remaining coils on the legs adjacent'thereto to form a pair of windings for deflecting the beam of a cathode ray tube in transverse directions.

2. In a deflection yoke for a cathoderay tube,

, a magnetic core having four legs. arranged to form a square, a winding disposed-on each'leg comprising a pair of-outer coils and aplurality with the outer coils on the legs adjacent to said parallel legs to form a pair obcircuitsforder fleeting the-beamof a cathode ray tube in transverse directions.

- 3. In adeflectionyoke for a cathodeqray tube, a magnetic core comprising-four legs arranged to form. a rectangle,-.series connected windings disposed .on opposite of said legs, said windings producing a non-linear field in a directionqparallel; with saidopposite legs, and means-for increasing the linearity of said field comprising a coil disposed on one of the legs transverse to said opposite leg and connected in series-with said windings.

4. 'I'hecombination, in a-defiection yokefor a cathode ray tube-of a magnetic core having four legs arranged to form EI'LCtflDEZIGuGflTiRUY connected windings disposed on opposite-ofsnid legs,said windings producing a non-linear field-in a direction parallel with said opposite'leg'e; and means for increasing the linearity of said'field comprising a pair of:coils disposedzon one. ofathe legs transverse-to said'opposite legs vandconncoted in series with said windings, said coils being con-- nected in said series circuit to establish oppos ing magnetic fields.

5. In combination, in a deflection yoke for a cathode ray tube, a magnetic core comprising four legs arranged to form a rectangle, serially connected windings disposed on opposite of said legs, said windings producing a non-linear field in planes parallel with said opposite legs, means for increasing the linearity of said field comprising two pairs of coils disposed respectively on the legs transverse to said opposite legs and connected in series with said windings, the coils of each of said pairs being connected in said series circuit to establish opposing magnetic fields.

6. In a deflection yoke for a cathode ray tube, the combination comprising a magnetic core having four legs arranged to form a rectangle, a plurality of coils supported on each of said legs, the outer coils on each of said legs being connected in series circuit with the remaining coils on the legs adjacent thereto to form a pair of windings for deflecting the beam of a cathode ray tube in transverse directions, said outer coils being connected in said series circuit to establish opposing magnetic fields.

7. In a deflection yoke for a cathode ray tube, the combination comprising a magnetic core having four legs arranged to form a square, a winding disposed on each leg comprising a pair of outer coils and a plurality of intermediate coils, said outer coils comprising a greater number of turns than said intermediate coils, the intermediate coils on parallel of said legs being connected in series with the outer coils on the legs 

